Review: Allelochemicals as multi‐kingdom plant defence compounds: towards an integrated approach

Abstract

The capability of synthetic pesticides to manage weeds, insect pests and pathogens in crops has diminished due to evolved resistance. Sustainable management is thus becoming more challenging. Novel solutions are needed and, given the ubiquity of biologically active secondary metabolites in nature, such compounds require further exploration as leads for novel crop protection chemistry. Despite improving understanding of allelochemicals, particularly in terms of their potential for use in weed control, their interactions with multiple biotic kingdoms have to date largely been examined in individual compounds and not as a recurrent phenomenon. Here, multi‐kingdom effects in allelochemicals are introduced by defining effects on various organisms, before exploring current understanding of the inducibility and possible ecological roles of these compounds with regard to the evolutionary arms race and dose–response relationships. Allelochemicals with functional benefits in multiple aspects of plant defence are described. Gathering these isolated areas of science under the unified umbrella of multi‐kingdom allelopathy encourages the development of naturally‐derived chemistries conferring defence to multiple discrete biotic stresses simultaneously, maximizing benefits in weed, insect and pathogen control, while potentially circumventing resistance. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Diversity of resident plant communities could weaken their allelopathic resistance against alien and native invaders

“…The latter could be due to traits that allow the plants to quickly take up available resources, resulting in high intrinsic growth rates (Dawson et al 2011;Zhang and van Kleunen 2019). It has also been suggested that the high competitive ability of some invasive plants could be achieved by suppression of germination and growth of neighboring plants by allelochemicals (Baker 1974;Callaway and Aschehoug 2000;Hickman et al 2020). In support of this idea, Kalisz et al (2021) showed that of the 524 invasive plant species in their database, at least half have known allelopathic effects.…”

Natural toxins: environmental contaminants calling for attention

“…2 Faculty of Science, RECETOX, Masaryk University, Brno, Czech Republic. 3 Environmental Analytics, Agroscope, Switzerland.…”

“…Some show low acute toxicity like the glycoalkaloids in potato or isoflavones in clover, medium toxicity as linamarin in cassava and coniin in poisonous hemlock, while some are very toxic like ricin in castor beans and the cyanotoxin saxitoxin produced by blue-green algae (Table 1). Many of these compounds may have or have had a function as natural defense chemicals in order for the toxin producing organism to compete with other species, and to protect itself against herbivoric and pathogenic attacks and other stressors [3,4].…”

Success, despite another plague year

“…The potential effects of an imminent ban of glyphosate in Mexico are discussed in a perspective 55 . The potential use of allelochemicals in integrated weed management is reviewed 56 …”